An azimuth thruster is a configuration of marine propellers placed in pods that can be rotated to any horizontal angle (azimuth), making a rudder unnecessary. These give ships better maneuverability than a fixed propeller and rudder system.

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There are two major variants, based on the location of the motor:[citation needed]

Mechanicaltransmission, which connects a motor inside the ship to the outboard unit by gearing. The motor may be diesel or diesel-electric. Depending on the shaft arrangement, mechanical azimuth thrusters are divided into L-drive and Z-drive. An L-drive thruster has a vertical input shaft and a horizontal output shaft with one right-angle gear. A Z-drive thruster has a horizontal input shaft, a vertical shaft in the rotating column and a horizontal output shaft, with two right-angle gears.

Mechanical azimuth thrusters can be fixed installed, retractable or underwater-mountable. They may have fixed pitch propellers or controllable pitch propellers. Fixed installed thrusters are used for tugs, ferries and supply-boats. Retractable thrusters are used as auxiliary propulsion for dynamically positioned vessels and take-home propulsion for military vessels. Underwater-mountable thrusters are used as dynamic positioning propulsion for very large vessels such as semi-submersibledrilling rigs and drillships.

The BPCDixmude manoeuvering in Jounieh bay; the wake at the aft is perpendicular to the ship, indicating the use of her azimuth thrusters.

Primary advantages are electrical efficiency, better use of ship space, and lower maintenance costs.[citation needed] Ships with azimuth thrusters do not need tugboats to dock, though they still require tugs to maneuver in difficult places.

The azimuth thruster using the Z-drive transmission was invented in 1950 by Joseph Becker, the founder of Schottel in Germany, and marketed as the Ruderpropeller. Becker was awarded the 2004 Elmer A. Sperry Award for the invention.[1] This kind of propulsion was first patented in 1955 by Pleuger.[2]